Composite facestocks and liners

ABSTRACT

Film-forming means are coextruded to form all plastic multilayer liners and facestocks for pressure-sensitive labels, tapes, decals, signs, bumper stickers, and other products formed from sheet and roll stock. Fill means in a change for the liner coextrusion affects stiffness and dimensional stability of the liner and/or affects the roughness of a liner face or faces. The film materials of the layers of the constructions are selected according to the cost/benefit characteristics of candidate materials considering the functional or operational requirements of the layer in question.

This application is a divisional application of copending U.S. patentapplication Ser. No. 088,402, filed Aug. 24, 1987 now U.S. Pat. No.4,888,075, which is a divisional application of U.S. patent applicationSer. No. 853,772, filed Apr. 18, 1986, now U.S. Pat. No. 4,713,273,which is a continuation-in-part of U.S. patent application Ser. No.699,204, filed Feb. 5, 1985, now abandoned.

BACKGROUND OF THE INVENTION

It has long been known to manufacture and distribute pressure-sensitiveadhesive stock for display products such as labels and signs byproviding a layer of face material for the label or sign backed by alayer of pressure-sensitive adhesive which in turn is covered by arelease liner. The liner protects the adhesive during shipment andstorage. With specific reference to labels, the liner also allows forefficient handling and dispensing of individual labels which have beendie-cut from the layer of face material while leaving the liner uncut.

Many label and sign applications require that the face material be apolymeric film material which can provide properties lacking in paper,such as weatherability (for outdoor signs), strength, water resistance,abrasion resistance, gloss and other properties. Because material costsin the manufacture of such film facestocks are relatively high, thedesirability of reducing material costs without sacrifice of quality haslong been apparent, but little or nothing has been accomplished towardthis end.

Because the cost of paper generally compares favorably with the cost offilm materials, and because paper liners also have other highlydesirable characteristics, the liners used with film facestocks havegenerally comprised paper web stock coated with a very thin layer ofsilicone-based release agent. The paper web's outer or "back" face hasthe roughness required to track well on the smooth steel rolls used inhigh speed manufacturing. The inner release-coated face of the paper webis uneven enough to slightly roughen the surface of the adhesiveprotected by the liner, thus preventing subsequent air entrapment andbubble formation between label and container in labeling applications.

However, paper readily absorbs and desorbs moisture, leading to curlingand distortion of film facestock with which a paper liner is used. Thisis particularly a problem with sheet facestock used, say, for signs anddecals. Moisture absorption and curling have been reduced to a degree bycoating the outside face of the paper liner with a thin moisture barrierlayer of film material, but edge absorption or gradual moisturetransmission through the moisture barrier itself have largely thwartedefforts to eliminate the problem of curling of the liner and consequentdistortion of the film facestock.

Another disadvantage of paper is its relative mechanical weakness. Thisis particularly a drawback in high speed packaging of high volumeconsumer products where labeling machinery must dispense rolls ofliner-carried labels at high speed. A break in the paper liner forcesshutdown of the entire packaging line until the labeling operation isproperly reset. As line speeds have continued to increase in recentyears, the severity of this problem has led some mass packagers tospecify that labels are to be carried on polyester film liner. The greatstrength of the polyester film eliminates the liner breakage problem,but at a price which reflects very much higher material costs than thoseassociated with paper.

THE PRESENT INVENTION

The present invention opens the way to substantial cost savings in themanufacture of film facestocks while at the same time maintaining thedesirable characteristics of the film facestocks which have been usedprior to this invention. In a word, costs are greatly reduced at littleor no sacrifice of quality, and even with a gain in quality in someinstances.

In another aspect, the present invention replaces paper liner stock byliner stock of polymeric film material. This is done in such a way as tosimulate those characteristics of paper that provide for good webtracking and adequate prevention of the problem of air entrapment andbubbling. At the same time, the problems of curling and paper breakingare eliminated because the film material used according to the inventionis inherently moisture-insensitive and is much stronger than paper. Allthis is accomplished at little or no increase over the cost associatedwith paper liners. In a word, quality is greatly improved at little orno increase in costs, and even with a reduction in costs in someinstances.

In the drawings, all of which are highly diagrammatic, FIGS. 1 and 2 arefragmentary cross sections of two different liner constructionsembodying the invention;

FIGS. 3A-3D illustruate certain steps in the manufacture and use ofproduct embodying the invention;

FIG. 4 is a fragmentary cross section of a prior-art liner;

FIGS. 5-7 are fragmentary cross sections of three different facestockconstructions embodying the inventions; and

FIG. 8 illustrates a manufacturing step related to the facestock of theinvention.

Liner stock constructions illustrating the invention will be describedfirst. A prototypical example is illustrated in FIG. 1, which shows amulti-layer web construction generally indicated by the referencenumeral 10. The multilayer construction 10 includes a core or base layer12, and skin layers 14 and 16. A first face, generally indicated by thereference numeral 18, is the outer or "back" face of the liner stock.This face is identified with the side of the web that will contact andbe guided by the smooth steel rolls of the manufacturing line in whichthe liner stocks is to be employed. A second face, generally indicatedby the reference numeral 20, is the inner face of the liner. This faceis identified with the side of the liner nearest the adhesive to beprotected by the liner.

The layers 12, 14, and 16 comprise polymeric film materials and areformed by simultaneous extrusion from any suitable known type ofcoextrusion die such as, for example, a Cloeren "vane" die heretoforeemployed, for example, to form multilayer films used in food packagingapplications. The layers 12, 14, and 16 are firmly adhered to each otherin a permanently combined state to provide a unitary coextrudate for allthree layers, although any one or more polymers or copolymers which willform firmly adherent films when coextruded and which are otherwisesuitable, particularly in respect of heat resistance and hardness, maybe employed, such as polypropylene, acrylonitrile butadiene styrene,nylon, polystyrene, and other appropriate extrudable thermoplastics.

The core or base layer of the coextrudate is loaded with filler materialto provide a continuous phase of the film-forming material itslef and adiscontinuous phase of the filler material. Thus, in the example of FIG.1 the core or base layer 12 is loaded with mica filler 22 in naturallyoccurring platelet form. Mica is presently preferred as filler for itsheat resistance and for its flatness which enhances its contribution tofilm stiffness, but other fillers having a high aspect ratio (ratiobetween greatest and least dimensions) may be used, such aswollastonite, glass fibers, talc, graphite platelets, graphite fibers,boron fibers, sapphire fibers steel fibers, or polymeric or polyesterfibers, e.g., DuPont's Kevlar. The filler comprises between about 5% and40% by weight of the core layer and is mixed into the charge offilm-forming resin which is fed to the extrusion orifice associated withformation of the core layer 12.

The naturally occurring platelet form of the mica 22 is seen edge-on inthe diagrammatic illustration of FIG. 1, the individual platelets havingsignificant width as well as length. These platelets orient themselvesin the machine direction when passing through the extrusion die so as tobe oriented lengthwise of the resulting extrudate as indicated in thedrawing. These platelets contribute significantly to enhancing the heatresistance or dimensional stability and the stiffness of the extrudatefilm. The mica as used in commerical manufacture is a mined productcontaining "impurities" of inorganic ore particles such as quartz orfeldspar which tend to be prune-shaped or lumpy rather than beingacicular (non-rounded) or plate-like as is the mica. These lumpyparticles 22a may include some particles whose bulk approaches orexceeds a majority of the thickness of the layer 12 in which they arecontained. The particles 22a, and particularly the larger of suchparticles, act through the skin 16 to roughen or contribute to theroughness of the outer face thereof. They may also similarly contributeto the roughening of the outer face of the layer 14, i.e., the back faceof the liner. Such filler is mixed into the charge of film-forming resinwhich is fed to the extrusion orifice associated with formation of theskin layer 14.

In most applications, the extrudate is hot-stretched, a stretch ratio ofabout 5:1 being employed or a somewhat lower or higher ratio may beemployed, say, from about 4:1 to about 9:1, Thus, using a 5:1 ratio,overall extrudate thickness may be reduced from say 16 mils at theextruding nozzle to say 3.2 mils after stretching. Typical finalthicknesses of the skin layer 14 and 16 may be from about one-tenth of amil to several tenths of a mil, or even a mil or more, with the core 12making up the remainder of the thickness. Stretching causes voids 29 toform adjacent to or around the lumpy particles 22a and, to some extent,at the mica platelets 22. The particles act as "seed" for thediscontinuous voids. The voids form in a one-to-one relationship withthose of the particles that do act as seeds, so that each void has itsown associated particle. Occasionally the size and position of eithertype of particle as compared to film thickness may be such that voidformation incident to stretching also causes rupture of a skin layer sothat the fill particle is exposed at one face of the construction, as isshown in connection with a specific lumpy particle 22b in FIG. 1. Thismay occur at either face. It is to be noted, however, that the voids 29are isolated from each other. The roughening effect of the filler mayoccur either indirectly through the bumpiness caused by the fillerdistorting the extruded film in the thickness direction or directly bybreakthrough of filler particles to the surface as in the case ofparticle 22b.

The thicknesses mentioned above are not intended to be limiting, and itis contemplated that in general overall thickness of the strecthedextrudate may vary from half a mil or less to 10 or more mils. To date,constructions of from 1.5 to 6.5 mils have been made.

When the extrudate is to be hot-strecthed, and in accordance withaccepted hot-stretching techniques, after extrusion and initial chillingthe extrudate is reheated to say 275° F. and stretched at the nipbetween two rolls, the second of which turns at a defined multiple ofthe turing speed of the first, to thereby define the desired stretchratio. The stretched extrudate is then further heated to say 300° F. tothereby "heat set" the stretched films.

The use of mica platelets or other high-aspect-ratio fillers in thecoextrudate of the present invention is mentioned above. So far as weare aware, it is new to use mica platelets or other high-aspect-ratiofiller particles to remove unwanted limpness from an extruded flexiblethermoplastic film, even a momoextrusion. Also, it is believed to benovel, even as to a non-extrusion, to provide a multiphase film whereinhigh-aspect-ratio particles, as distinguished from circular particlessuch as calcium carbonate, act as "seeds" for discontinuous voidformation.

Rather than as a byproduct of the mining of acicular orhigh-aspect-ratio filler such as mica, circular filler may bedeliberately included in the extrudate in the presence or absence of anacicular filler. for example, relatively fine cicular particles may beadequate to provide desired roughening for very thin extrudates, sothat, for example, relatively fine calcium carbonate particles or silicaor other relatively fine circular particles may be used in thincoextrudates or monoextrusions, with the dimensional relationships ofparticles and film being chosen so that roughening is accomplished.

It will be understood by those in the industry that at least somematerials used as fillers may also be used in small amounts asadditives, such as a coloring agent, an antistatic, an antioxidant, awhitening or coloring means, or for other similar purposes. However,such other uses do not generally affect the mechanical behavior ornature of the formed film, and do not represent filling of the film ascontemplated by the invention.

Release means is provided on or at the second face or inner side 20 andmay comprise a release coating 26 of silicone or other materialproviding release characteristics (e.g., fluorocarbon) on the skin layer16, or a release surface presented due to the presence of releasecomponents in te skin 16 itself. When a silicone release coat 26 isused, the skin layer 16, being of polypropylene or other material havingthe good silicone holdout properties of plastics, helps assure goodrelease action and avoidance of blocking by substantially acting as astop against absorption of the release layer into the core layer andthereby maintaining the uniformity of the release coating 26 after it isapplied.

FIG. 2 illustrates a liner stock construction 110 which is similar inmany ways to the construction 10 of FIG. 1, and in which similarcomponents are numbered as in FIG. 1 but with the additon of 100 to eachreference number. In the construction 110 of FIG. 2, however, there isno separate skin layer on the "back" side or first face 118. Instead,the first face 118 comprises the outer or exposed side of the core layer112.

In the constructions shown in FIGS. 1 and 2, the first and second facesare roughened by the mechanical effect of the filler material,predominantly the lumpy particles 22a or 122a. Each face should have aroughness of at least about 10 Sheffield units.

As to the minimum roughness of the back face (such as face 18 or face118) which contacts the steel guide rolls on a manufacturing line, ithas been found that the coefficient of friction of the film, as measuredagainst glass, increases with decreasing roughness, so that one wouldexpect the smoothest film, having the highest coefficient of friction,to track the best. Surprisingly however, when roughness of the back faceis reduced to less than about the mentioned minimum Sheffield value,tracking of the film deteriorates with decreasing roughness, even thoughthe coefficient of friction is being increased.

As to the minimum roughness of the other face (such as face 20 or 120),it has been found that at least the mentioned minimum Sheffield value isnecessary to avoid problems of air entrapment during label application,with higher levels being required in some instances, as will be morefully discussed below.

Both the continuous phase of the core layer 12 (or 112) and thediscontinuous phase of filler material 22 (or 122) are dimensionallystable under conditions of moisture absorption or desorption such as mayoccur during long periods of warehousing in humid or dry climates. Thesame is true of the skin layer 14 of FIG. 1. The skins 16 and 116 aresimilarly stable. The dimensional stability of each liner constructionis therefore independent of humidity conditions and the constructiontherefore remains flat (not curled or distorted) under differenthumidity conditions as encountered at different geographic locations orat the same location at different times. The core layers, as well as theskins of the constructions 10 and 110, are free of all but isolatedvoids and are substantially free of connected or continuous-phase voidsso that the web also remains flat and undistorted under varying webtemperature conditions as encountered in hot air drying of inks orcoatings for facestocks with which the liner is used.

One accepted test of flatness uses a test sheet of the stock beingtested which is 36 inches long and 24 inches wide. The sheet isconsidered flat if it exhibits a lift of no more than 1/4 inch at anycorner, edge or interior area portion under the humidity condition orconditions encountered. Such a stock may test "flat" at say 50% relativehumidity, a humidity level commonly used at present for quality testingat the factory, but may fail the same test under greater or lesserhumidities, particularly where an extreme change in humidity isencountered in the field. In contrast, test sheets of the constructionsof the present invention, such as constructions 10 and 110, exhibit lessthan 1/8 inch lift, and in fact little or no discernible lift, under anyhumidity condition that can be expected to be encountered, say from 5%to 100% relative humidity.

In the manufacture of the liner of FIG. 1, charges A, B, and C,corresponding respectively to layers 16, 12, and 14, may be prepared forcoextrusion through a coextrusion die 30, as schematically illustratedin FIG. 3A. By preselection, charge A contains no filler, charge Bcontains filler within the ranges specified earlier, and charge Ccontains no filler or a lower degree of filler. Upon coextrusion throughthe die 30, the charges form a multilayer extrudate to which thesilicone release coating 26 (FIG. 1) may be applied at station R toprovide the multilayer web construction 10. Or, the charge for layer 16may include release components to inherently generate a release surfaceat the outer face of the layer. If the release coating 26 is applied, itis dried or cured following application by any suitable means (notshown). Prior to application of the release coating at station R, theformed films may be hot-stretched in a known manner to provide machinedirection orientation of the liner 10. This is generally done for "rollliner," but generally not for "sheet liner," which terms are definedbelow.

In accordance with well-known practice in the industry, the release faceof a release liner may be coated with a layer of pressure-sensitiveadhesive for subsequent transfer of the adhesive to the facestock withwhich the liner is employed. When the facestock is combined with theliner, the adhesive is joined to the facestock. Later, the liner isremoved to expose the adhesive, which now remains permanently joined tothe facestock.

Thus, as indicated in FIG. 3A, adhesive may be applied at station Sfollowing drying or cure of the release coat previously applied atstation R. This may be a tandem coating operation, or the adhesivecoating may be on a separate coating liner. Or, the adhesive may beapplied at some later time prior to the combining of the release liner10 with facestock. The combining of the liner with a facestock 32 isdiagrammatically illustrated in FIG. 3B. FIG. 3C diagrammaticallyillustrates the die-cutting of the facestock 32, at a station T, into aseries of pressure-sensitive labels 34 carried by the release liner 10.As is well known, this step is usually performed by rotary cutting diesand involves the stripping of the matrix (not shown) of waste or trimsurrounding the formed labels. FIG. 3D illustrates the application ofthe labels 34 to passing workpieces 36 by use of a peelback edge 38 todispense the labels 34 by progressively removing the liner from them ina well-known manner to thereby expose the adhesive side 39 of the labelsand project the labels into contact with passing workpieces.

FIG. 4 diagrammatically illustrates a film of conventional or prior artfacestock 32 with pressure-sensitive adhesive 40 permanently combinedtherewith, such facestock being employed in the methods or procedures ofthe invention at the stage illustrated at the right end of FIG. 3B orthe left end of FIG. 3C. At this stage, the adhesive 40 (not shown inFIGS. 3A to 3D) may be releasably carried on the liner 10 of theinvention (on or with which it may have been previously coated orcombined, as by the previously mentioned coating step at station S).Alternatively, the adhesive 40 may have been directly coated on orcombined with the facestock 32 prior to the combining of the facestockwith the liner 10. The liner 10 is not shown in FIG. 4; if it were, thisfigure would illustrate one aspect of the present invention, namely, thecombining of a conventional type of facestock with a coextruded liner ofthe type taught herein.

Where the adhesive contacts the inner face of the liner 10, either atstation S or upon the combining of the facestock with the liner 10 ifthe adhesive is originally coated on or combined with the facestock, theroughness of face 20 of the liner 10 is imparted to the adhesive. Whenthe adhesive is later exposed, as at face 39 in the step illustrated inFIG. 3D, the exposed adhesive face exhibits the roughness imparted byface 20 of the liner. This roughness performs an important function ineliminating or minimizing air entrapment during label application andthe resultant forming of blisters or high spots on the applied label.

As indicated above, a roughness of at least about 10 Sheffield units atthe adhesive-contacting face is required for avoiding or minimizing airentrapment during label application. However greater roughness generallyis better from the standpoint of avoiding air entrapment, androughnesses of 150 or more may be necessary in some applications,depending on such factors as bottle surface, bottle shape, amount, typeand temperature of adhesive, and line speed.

Meanwhile, the reverse or back face 18 of the liner 10, also roughenedat least to the specified minimum degree, tracks smoothly and securelyand without slippage on the steel idler rolls and drive rolls (notshown) used to guide or drive the liner 10 in any of the stages of FIGS.3A to 3D.

It will be understood that the operations shown in FIGS. 3A to 3D willoften be done at different locations by different manufacturers, or theymay be combined. For example, the steps of FIG. 3A may be performed by aliner and adhesives manufacturer, the steps of FIGS. 3B and 3C may beperformed by a label manufacturer on one continuous pass, rather thanbeing interrupted by a wind-unwind sequence as illustrated, and thesteps of FIG. 3D may be performed by a packager of manufacturedproducts.

Facestock which is formed into labels is usually wound and unwound inroll form and is therefore one form of what is known as "roll stock" or"roll facestock," and the accompanying liner is called "roll liner."Facestock in roll form may also be utilized as continuous tape. Theforegoing relates to roll stock and roll liner. In many respects, theinvention also applies, however, to "sheet liner" used with "sheetstock" which might be formed as indicated in FIGS. 3A and 3B but wouldthen be cut into sheets and decorated (by screen printing, for example)for use as decals, bumper stickers, thermal die-cut signs, and the like.Materials and procedures used for sheet stock and sheet liner may be thesame or may differ to some degree from those used for roll stock androll liner, but the principles of the construction and manufacture ofthe liner can be similar whether it be liner for roll stock or sheetstock.

The release liner 110 of FIG. 2 may be roll liner or sheet liner. Thisliner 110, may be extruded in a manner similar to that indicated in FIG.3A, but with only two charges corresponding to the layers 116 and 112.The charge corresponding to layer 116 has no filler and the chargecorresponding to layer 112 includes the filler 122, 122a mixed therein.

The thickness of liner 10 or 110 may be say 3.2 mils with the skinlayers 14 and 16 or 116 each being one or several tenths of a mil thickand the core or base 12 or 112 making up the remainder.

Available mined mica supplies with their "impurities" may have thefollowing typical particle size distribution:

                  TABLE I                                                         ______________________________________                                        Particle Size Distribution of Mica                                            (Percent By Weight Of Sample On Or Through Screen)                            Screen Size                                                                             Mica No. 1   Mica No. 2                                                                              Mica No. 3                                   ______________________________________                                        +200      0.4          0.0       5.0                                          +325      15.8         38.4      23.4                                         -325      83.4         61.6      71.6                                         ______________________________________                                         Note:                                                                         + = retained on screen                                                        - = through screen                                                            Mica No. 1 = acicular                                                         Mica No. 2 = cicular                                                          Mica No. 3 = same as 2 with different grading                            

Since the mesh opening of a 200 mesh screen is 2.9 mils and that of a325 mesh screen is 1.7 mils, it can be seen that the larger particles inthese samples have dimensions exceeding the majority of core or basethickness or even the core thickness itself. (Mica number 3 in the abovetable is generally unsatisfactory due to 5% content of particlesretained on a screen with 2.9 mil mesh openings). Thus it will beunderstood that considerable surface roughness may be "thrust on " amanufacturer utilizing these fillers to a point where the question isnot one of achieving desired minimums but of minimizing roughness. Forexample, a back face roughness exceeding a relatively low Sheffieldvalue will cause a "dit" (dimple plus pit) problem when the liner iscombined with a very smooth soft facestock such as flexible polyvinylchloride and then wound for storage or transport, since the facestockdirectly contacts the rough back face in the wound condition. Other onlysomewhat less dit-prone facestocks include semirigid polyvinly chloride,polyethylene, and polypropylene, and these may tolerate Sheffieldroughnesses of up to about 150. Facestocks of polystyrene, polycarbonateand thermoplastic polyester are more capable of resisting the formationof dits up to Sheffield roughnesses of about 300 or more. Facestocksintended to have rough surfaces that wholly or partially mask any ditsthat are formed will of course tolerate considerable roughness insofaras the formation of dits is concerned.

In accordance with generally established post-extrusion finishingpractice, the coextrudate may pass from the extrusion nozzle though anip formed by chilled finishing rolls, often a polished steel roll and asilicone rubber roll. The extrudate face on the steel roll side receivesa gloss finish and the opposite face receives a matte finish. Generallythe face with the matte finish is the guide roll contacting face, suchfirst face 18 or 118, while the opposite face, such as second face 20 or120, is the face with the gloss finish. However, both sides may be givena matte or a gloss finish if desired.

In some circumstances, roughness at a face, particularly the first face,may be provided simply by the matte finishing or embossing effect of apost-extrusion roll of the coextruder. In other words filler may not benecessary to the required roughening effect at a face, and the situationbecomes one of avoiding over-roughening due to use of filler.

It will therefore be understood that, looked at from the manufacturingstandpoint of minimizing roughening when dit-prone facestock is to beemployed or when for other reasons avoidance of over-roughening in agiven application is a concern, the invention involves the concept ofattenuating the roughening effect of the filler by coextruding at leasta second unfilled or relatively unfilled charge along with the filledcharge to form the resulting coextrudate, with the second charge forminga skin that tends to smooth the bumps caused by the filler. Generally,the thicker the formed skin, the greater the smoothing action. Thesmoothing may result from the greater "evening out" effect of thethicker skin, and/or from the accomplishment of full coverage withoutskin rupture over filler particles which would be otherwise exposed,such as particle 22b in FIG. 1.

Turning now to facestock, prototypical examples of film facestocksillustrating the invention are seen in FIGS. 5 and 6. In FIG. 5, amultilayer web construction, generally indicated by the referencenumeral 50, comprises a coextrudate including a core layer 52, a skinlayer 54 on the face side of the coextrudate, and a skin layer 56 on theinner side of the coextrudate opposite the face side. Combined on theinner side of the coextrudate is a pressure-sensitive adhesive layer 58.In FIG. 6, a multilayer web construction, generally indicated by thenumeral 50a, comprises layers 52a, 54a, 56a, and 58a generallycorresponding to the layers 52, 54, 56, and 58 in FIG. 5. However, inFIG. 6, tie layers 53 join the core layer 52a to the skin layers 54a and56a.

The coextrudates of FIGS. 5 and 6 are similar to the previouslydescribed liner stock in that they comprise polymeric film materials,are formed by simultaneous extrusion from a suitable known type ofcoextrusion die, and are adhered to each other in a permanently combinedstate to provide a unitary coextrudate. The FIG. 5 construction is usedwhen the materials of the core and skins are such that these layersfirmly adhere or bond to each other when coextruded as adjacent filmlayers. The FIG. 6 construction, with the tie layers 53, is used whenthe core and skin materials do not sufficiently adhere or bond to eachother when they are extruded together. Generally, the construction ofFIG. 5 is presently used for roll film facestock and that of FIG. 6 forsheet film facestocks because, while polyethylene is presently preferredas the core material for both applications, roll film facestocks andsheet film facestocks generally use different skin materials, and thepresently preferred material for the skin of the roll film facestock(ethylene vinyl acetate) is compatible with polyethylene in respect ofinherent adhesion or bonding, while the presently preferred material forthe skin of the sheet film facestock (polyvinyl chloride) is not.

The materials of the layers of constructions 50 and 50a are selectedaccording to the cost/benefit characteristics of candidate materialsconsidering the functional or operational requirements of the layer inquestion. An important concept of the invention is the application ofthis principle to the manufacture of facestock by forming the facestockas a coextrudate of materials so selected.

Thus, the facestock at its outside surface may require highweatherability and printability and good uniformity and control ofsurface texture, whether gloss or matte, whereas these qualities eitherare not necessary or are required in far lesser degree in the core ofthe facestocks. The latter, however, must be such as to give thefacestock opacity and the desired degree of stiffness, as well assufficient body and strength, and represents generally the great bulk ofthe total material used in the construction. The stiffness of this corematerial should be between about 10 and 100 Gurley. The inner surface ofthe film coextrudate must give good anchorage for the adhesive.

The presently preferred material for the core layers 54 or 54a in manyfacestock applications is polyethylene of low, medium, or high densityof between about 0.915 and 0.965 specific gravity. This is a relativelylow cost, extrudable film-forming material whose stiffness (rangingthrough decreasing degrees of flexibility to semirigid) may bedetermined by the density selected, and whose body and strength aresufficient for most uses. Polyethylene of lower densities, down to aspecific gravity of 0.890, may be employed for greater flexibility.

Another preferred material for the core layers 54 or 54a ispolypropylene (or a propylene copolymer) having a flex modulus range ofbetween about 130,000 and 250,000 psi at 73° F., depending on thestiffness desired.

Polyethylene vinyl acetate is generally the presently preferred materialfor both skin layers 54 and 56 in roll film applications, whilepolyvinyl chloride is generally the presently preferred material forboth skin layers 54a and 56a in sheet film applications. A suitableresin for tie layer 53 in this instance is "CXA", marketed by DuPont.Another material for forming tie layers is "Plexar" marketed by ChemplexCo. Other specific materials are also available for performing the tyingfunction in coextrusion operations. The outer surface of the skin layer54 or 54a is corona-treated in a known manner to increase printabilityof the skin.

The preferred identity of the outer and inner skin layer material atpresent is partly a choice of convenience in reduction to practice, andit is contemplated that these materials often will not be identical inactual manufacture. For example, polyethylene vinyl acetate might be thematerial of choice for the outer skin, but polyethylene acrylic acidmight be used on the inner skin for better anchorage to, say, an acrylicadhesive of choice.

Other materials for the skin layers include meltable film-formingsubstances used alone or in combination, such as polyethylene methylpolyacrylic acid, polyethylene ethyl acrylate, polyethylene methylacrylate, acrylonitrile butadiene styrene polymer, nylon, polybutylene,polystyrene, polyurethane, polysulfone, polyvinylidene chloride,polypropylene, polycarbonate, polymethyl pentene, styrene maleicanhydride polymer, styrene acrylonitrile polymer, ionomers based onsodium or zinc salts of ethylene/methacrylic acid, polymethylmethacrylates, cellulosics, fluoroplastics, polyacrylonitriles, andthermoplastic polyesters.

While the foregoing examples of facestocks have employed skin layers oneach side of the core, there are instances where a skin layer isemployed only on the outer side of the construction, such as theconstruction 60 shown in FIG. 7, which employs the single skin layer 66on the outer side of a core layer 62. In this instance, thepressure-sensitive adhesive layer 68 is directly adjacent the corelayer. For example, such a construction could be used for themanufacture of high durability labels. Material presently preferred forthe core layer in such instance is polyvinyl chloride or acrylonitrilebutadiene styrene, and for the skin layer, polyvinylidene fluoride.

It will be understood from the foregoing that multilayer film facestockshave been provided having a relatively thick core layer of polymericfilm material which contributes the majority of the stock's dimensionalstability and stiffness, having a cojoined, relatively thin,ink-printable skin layer at least at the face side of the construction,and having a pressure-sensitive adhesive layer combined at the sides ofthe construction opposite the face side. From a method standpoint, thisis accomplished by coextruding a plurality of at least two charges offilm-forming resin to form a coextrudate having a relatively thick corelayer and at least one relatively thin skin layer after preselecting thecharge for the core layer, as by selection of density or flex modulus,to provide the degree of stiffness suitable for the label or signapplication, and after preselecting the charge for the skin layer toprovide a skin adapted to the intended decorating process, and combiningthe coextrudate with a pressure-sensitive adhesive layer.

Thus, in the manufacture of the facestock 50 seen in FIG. 5, charges D,E, and F, corresponding respectively to layers 52, 54, and 56, may beprepared for coextrusion through a coextrusion die 70, as schematicallyillustrated in FIG. 8. Charge E for the core layer is preselected toprovide the suitable degree of stiffness, charge D is preselected toallow for good printability (usually following corona treatment of theformed film) and for weatherability if indicated, and charge F ispreselected for good adhesive anchorage. As previously indicated, oftencharges D and F for the skin layers may be the same, and in someapplications, the skin layer on the inner or adhesive side,corresponding to charge F, is eliminated. The coextrudate 54, 52, 56forming the facestock may be hot-stretched.

The coextrudate may be directly coated with the adhesive 58, or theadhesive 58 may be transferred from a liner with which the facestock iscombined. In particular, the coextrudate of cojoined facestock layers54, 52, 56 may be substituted for the facestock 32 of FIGS. 3B to 3D,and the adhesive 58 may be the adhesive applied at the coating station Sin FIG. 3A. The result is an all plastic facestock/liner combination inwhich both the facestock and liner are multilayered.

Instead of being coated or combined on the formed coextrudate as justdescribed, the adhesive 58 may be coextruded along with the film-forminglayers 54, 52, 56. The invention also contemplates simultaneouslyextruding both liner and facestock as by simultaneously extruding allthe charges A through F, together with a charge of adhesive 58, whichwould for example be extruded through an additional orifice adjacent tothe orifice for charge F. This would require provision of release meansfor the liner prior to contact of the liner by the adhesive.

The facestock construction 50a is manufactured in a manner similar tothe manufacture of facestock 50. The additional tie layers 53 arecoextruded along with the layers 52a, 54a, and 56a.

It should be evident that this disclosure is by way of example and thatvarious changes may be made by adding, modifying or eliminating detailswithout departing from the fair scope of the teaching contained in thisdisclosure. The invention is therefore not limited to particular detailsof this disclosure except to the extent that the following claims arenecessarily so limited.

What is claimed is:
 1. A method of economically manufacturing die-cutlabels or signs using roll or sheet facestock, comprising the steps ofproviding a plurality of at least two charges of film-forming resin,coextruding said charges to thereby form a construction in the form of amultilayer extrudate comprising a relatively thick core layer and atleast one relatively thin skin layer, the former layer providing themajority of the dimensional stability and stiffness of the construction,preselecting the charge for said core layer, as by selection of densityor flex modulus, to provide a degree of stiffness suitable for the labelor sign application, preselecting the charge for said skin layer toprovide a skin adapted to the intended decorating process, such asprintability, or surface performance characteristics, such asweatherability, of the facestock, and combining said extrudate with apressure-sensitive adhesive layer to form label or sign facestock,combining said facestock with a liner, die-cutting said facestock toform a label or sign releasably adhered to said liner and surrounded bya matrix of excess facestock material, and stripping said matrix ofexcess facestock material to utilize non-tearing self-supportingproperties of said material to pull said matrix away from the die-cutlabel or sign.
 2. The method of claim 1 in which at least one of saidsteps of preselecting the charge for said core layer and preselectingthe charge for said skin layer is accompanied by the selection of anon-olefinic film-forming resin for one or more of said layers.
 3. Themethod of claim 1 in which said steps of preselecting the charge forsaid core layer and preselecting the charge for said skin layer areaccompanied by the selection of film-forming resins such that thefilm-forming resin for the core layer has a melting point at least equalto the melting point of the film-forming resin for the skin layer. 4.The method of claim 1 in which said die-cutting of said facestockfollowing said coextruding step is performed in the absence of anyintervening step of biaxial stretching of said multilayer extrudate. 5.The method of claim 4 in which said steps of preselecting the charge forsaid core layer and preselecting the charge for said skin layer areaccompanied by the selection of film-forming resins such that thefilm-forming resin for the core layer has a melting point at least equalto the melting point of the film-forming resin for the skin layer. 6.The method of claim 4 in which at least one of said steps ofpreselecting the charge for said core layer and preselecting the chargefor said skin layer is accompanied by the selection of a non-olefinicfilm-forming resin for one or more of said layers.
 7. The method ofclaim 6 in which said steps of preselecting the charge for said corelayer and preselecting the charge for said skin layer are accompanied bythe selection of film-forming resins such that the film-forming resinfor the core layer has melting point at least equal to the melting pointof the film-forming resin for the skin layer.
 8. A method as in claim 1in which a series of labels are die-cut in said facestock and said stepof stripping said excess facestock material and pulling said matrix awayleaves the labels in spaced relation on the liner.
 9. The method ofclaim 8 in which said steps of preselecting the charge for said corelayer and preselecting the charge for said skin layer are accompanied bythe selection of film-forming resins such that the film-forming resinfor the core layer has a melting point at least equal to the meltingpoint of the film-forming resin for the skin layer.
 10. The method ofclaim 8 in which said die-cutting of said facestock following saidcoextruding step is performed in the absence of any intervening step ofbiaxial stretching of said multilayer extrudate.
 11. The method of claim10 in which said steps of preselecting the charge for said core layerand preselecting the charge for said skin layer are accompanied by theselection of film-forming resins such that the film-forming resin forthe core layer has a melting point at least equal to the melting pointof the film-forming resin for the skin layer.
 12. The method of claim 10in which at least one of said steps of preselecting the charge for saidcore layer and preselecting the charge for said skin layer isaccompanied by the selection of a non-olefinic film-forming resin forone or more of said layers.
 13. The method of claim 12 in which saidsteps of preselecting the charge for said core layer and preselectingthe charge for said skin layer are accompanied by the selection offilm-forming resins such that the film-forming resin for the core layerhas a melting point at least equal to the melting point of thefilm-forming resin for the skin layer.
 14. A method of economicallymanufacturing die-cut labels or signs using roll or sheet facestock,comprising the steps of providing a plurality of at least two charges offilm-forming resin, coextruding said charges to thereby form aconstruction in the form of a multilayer extrudate having a face sideand a back side, said multilayer extrudate including stiffening layermeans which contributes the majority of the stiffness of theconstruction, preselecting at least one of the charges, as by selectionof density or flex modulus, to provide said stiffening layer means witha degree of stiffness suitable for the label or sign application, andcombining said multilayer extrudate with a pressure-sensitive adhesivelayer and release liner to form linered label or sign facestock,die-cutting said facestock to form a label or sign releasably adhered tosaid liner and surrounded by a matrix of excess facestock material, andstripping said matrix of excess facestock material to utilizenon-tearing self-supporting properties of said material to pull saidmatrix away from the die-cut label or sign.
 15. The method of claim 14in which said step of preselecting the charges includes preselecting anon-olefinic film-forming resin for at least one of the charges.
 16. Themethod of claim 14 in which a series of labels are die-cut in saidfacestock and said step of stripping said excess facestock material andpulling said matrix away leaves the labels in spaced relation on theliner.
 17. The method of claim 14 in which said die-cutting of saidfacestock following said coextruding step is performed in the absence ofany intervening step of biaxial stretching of said coextrudate.